Stepper: Catch and show "name not declared" error (#1608)

* add: catch and show SourceRuntimeError

* refactor

* add: tests

* linting

* removed unused imports

* linting

* Revert "linting"

This reverts commit ff1c011.

* add comment for getExplanation

---------

Co-authored-by: Martin Henz <[email protected]>

src/stepper/__tests__/__snapshots__/stepper.ts.snap

@@ -4117,6 +4117,12 @@ f();
 "
 `;
 
+exports[`Test catching of undeclared variable error Variable not declared in block statement 1`] = `"Line 3: Name undeclared_variable not declared."`;
+
+exports[`Test catching of undeclared variable error Variable not declared in function declaration 1`] = `"Line 3: Name undeclared_variable not declared."`;
+
+exports[`Test catching of undeclared variable error Variable not declared in program 1`] = `"Line 2: Name undeclared_variable not declared."`;
+
 exports[`Test correct evaluation sequence when first statement is a value Irreducible second statement in block 1`] = `
 "{
   'value';

src/stepper/__tests__/stepper.ts

@@ -9,6 +9,11 @@ function getLastStepAsString(steps: [substituterNodes, string[][], string][]): s
   return codify(steps[steps.length - 1][0]).trim()
 }
 
+function getExplanation(steps: [substituterNodes, string[][], string][]): string {
+  // Explanation of the step is kept in index 2 of steps
+  return steps.map(x => x[2]).join('\n')
+}
+
 describe('Test codify works on non-circular abstract syntax graphs', () => {
   test('arithmetic', () => {
     const code = `
@@ -80,6 +85,36 @@ const testEvalSteps = (programStr: string, context?: Context) => {
   return getEvaluationSteps(program, context, options)
 }
 
+describe('Test catching of undeclared variable error', () => {
+  test('Variable not declared in program', async () => {
+    const code = `
+    undeclared_variable;
+    `
+    const steps = await testEvalSteps(code)
+    expect(getExplanation(steps)).toMatchSnapshot()
+  })
+
+  test('Variable not declared in block statement', async () => {
+    const code = `
+    {
+      undeclared_variable;
+    } 
+    `
+    const steps = await testEvalSteps(code)
+    expect(getExplanation(steps)).toMatchSnapshot()
+  })
+
+  test('Variable not declared in function declaration', async () => {
+    const code = `
+    function foo() {
+      undeclared_variable;
+    }
+    `
+    const steps = await testEvalSteps(code)
+    expect(getExplanation(steps)).toMatchSnapshot()
+  })
+})
+
 describe('Test reducing of empty block into epsilon', () => {
   test('Empty block in program', async () => {
     const code = `

src/stepper/stepper.ts

@@ -3,6 +3,7 @@ import type es from 'estree'
 
 import { type IOptions } from '..'
 import * as errors from '../errors/errors'
+import { RuntimeSourceError } from '../errors/runtimeSourceError'
 import { initModuleContextAsync, loadModuleBundleAsync } from '../modules/loader/moduleLoaderAsync'
 import { parse } from '../parser/parser'
 import {
@@ -37,7 +38,8 @@ import {
   isAllowedLiterals,
   isBuiltinFunction,
   isImportedFunction,
-  isNegNumber
+  isNegNumber,
+  prettyPrintError
 } from './util'
 
 const irreducibleTypes = new Set<string>([
@@ -3414,7 +3416,17 @@ export async function getEvaluationSteps(
     }
     return steps
   } catch (error) {
-    context.errors.push(error)
+    if (error instanceof RuntimeSourceError) {
+      // If steps not evaluated at all, add error message to the first step else add error to last step
+      if (steps.length === 0) {
+        steps.push([program, [], prettyPrintError(error)])
+      } else {
+        steps[steps.length - 1][2] = prettyPrintError(error)
+      }
+    } else {
+      context.errors.push(error)
+    }
+
     return steps
   }
 }

src/stepper/util.ts

@@ -6,6 +6,10 @@ import { RuntimeSourceError } from '../errors/runtimeSourceError'
 import { BlockExpression, Environment, Node, substituterNodes, Value } from '../types'
 import * as builtin from './lib'
 
+export function prettyPrintError(error: RuntimeSourceError): string {
+  return `Line ${error.location.start.line}: ${error.explain()}`
+}
+
 export function isBuiltinFunction(node: substituterNodes): boolean {
   return (
     node.type === 'Identifier' &&

src/validator/validator.ts

@@ -1,7 +1,6 @@
 import * as es from 'estree'
 
-import { ConstAssignment } from '../errors/errors'
-import { UndefinedVariable } from '../errors/errors'
+import { ConstAssignment, UndefinedVariable } from '../errors/errors'
 import { NoAssignmentToForVariable } from '../errors/validityErrors'
 import { parse } from '../parser/parser'
 import { Context, Node, NodeWithInferredType } from '../types'